Influenza virus, a Category C Biodefense pathogen, is a clinically important infectious agent with serious implications for human health. The threat of a pandemic as well as the potential for intentional contamination with highly pathogenic or genetically engineered virus strains provide strong rationales for further in-depth analysis of the immune mechanisms of viral control, the focus of this RFA. While vaccination against infection is believed to be mediated primarily by induction of serotype-specific neutralizing antibody, CD8 T cells have the potential to provide broad-based effectiveness against distinct viral serotypes. Our preliminary data identifies a novel memory CD8 T cell subset and suggests a potential link between memory CD8 T cells and B cells. These findings provide the foundation for this proposal aimed at learning the functional significance of the anatomical localization of memory CD8 T cell subsets and determining their protective capacity against influenza virus infection. The specific aims of the proposal are: [unreadable] [unreadable] Specific Aim 1. To characterize memory CD8 T cell subsets and determine their protective ability following influenza virus infection. The memory CD8 T cell population that develops following influenza virus infection is heterogeneous and comprised of multiple subsets based on phenotype and location. Our preliminary data suggested additional complexity by identifying a novel B220+ memory CD8 T cell subset. Experiments in this aim will focus on an in-depth phenotypic and functional characterization of memory CD8 T cell subsets including testing their ability to mount secondary responses and provide protection against influenza virus infection. [unreadable] [unreadable] Specific Aim 2. To visualize the primary and recall response to influenza virus infection in situ. The anatomical events that occur in situ during the immune response to primary or secondary influenza virus infection have not been described. We have developed techniques to allow visualization of endogenous antigen-specific primary and memory CD8 T cells in situ following infection. Preliminary data identify a novel population of memory CD8 T cells residing in the B cell zones of the lymph nodes and spleen following influenza virus infection and whether B220+ memory cells preferentially localize to these sites will be tested. The behavior of this population and other memory subsets to respond to infection will also be determined. In this way, a link will be established between the protective capacity of memory subsets and the anatomy of the secondary response. Overall, these studies will fill a significant gap in our knowledge regarding the role of memory CD8 T cells in controlling influenza virus infection. [unreadable] [unreadable] [unreadable]